1. Field of the Invention
The present invention relates to horn switches provided on steering-wheels of automobiles and wiring units used for horn switches, display apparatuses, interior wiring and others provided in vehicles such as passenger cars and the like.
2. Description of the Related Art
Conventional horn switches of such structure as shown in FIG. 10 are known. Namely a base plate 11 is disposed at the bottom inside a horn button 15 which is provided on a pad portion 9 at the center part of a steering wheel. A housing 12 is provided on said base plate 11. On the surface of said base plate 11, as shown in FIGS. 10 and 11, an electrode portion 14a is formed extending from the one end portion on said base plate 11 to the central portion in said housing 12. The other electrode portion 14b is formed extending from the other end portion on said base plate 11 in a shape of an arc so as to encircle said electrode portion 14a.
On the upper surface of said housing 12, a horn contact 16 is protruded therethrough, the upper portion of which contacts said horn button 15. On the under surface of the horn contact 16, a contact member 16a formed in a shape of a letter T at cross-sectional view is fixed. On the outer peripheral portion of said contact member 16a, a spring 17 is provided. A masking material M covers a partial area of the electrode portion 14a on the surface of said base plate 11 where a part of said spring 17 contacts.
Moreover, in various parts of a vehicle such as a horn switch, a base plate of a display unit or tail lamps and others, wiring connects the switch, the display portion, the tail lamps and others with the power source. It is troublesome in using a connectional electric wire to connect the end portions thereof with the given terminals. Especially, where a large number of terminals are disposed, there is a problem that the volume of electric wires becomes large and the apparatus becomes big as a whole. Therefore, printed wiring has been used for switches on steering wheels which are equipped with electric circuits. Further, as shown in FIG. 12, as an inexpensive method of manufacturing printed wiring, it is throughout that wiring patterns formed by ink for selective plating (which has properties of selectively plating inked portions) are transcribed on a base 61 made of resin. And then, wiring patterns 62 of copper, nickel and others are formed by applying electroless plating on pattern portions.
In a conventional horn switch as mentioned above, since the electrode portions 14a and 14b are formed on the same plane, the masking material M is required for preventing a portion of the spring 17 to contact the one electrode portion 14a on the base plate 11, which would cause the electrode portions 14a and 14b to be conductive.
Due to the thickness of the masking material M, the spring 17 partially contacts the other electrode 14b on the base plate 11. Also, the contact portion of the spring 17 with the other electrode 14b on the base plate 11 can not be enlarged due to the masking material M. These are problems. And another problem was to increase the manufacturing cost by using the masking material M.
In the foregoing method of preparing printed board with wiring patterns and using the same, there was a problem that printed boards used for electric circuit were expensive. Also, the number of parts to be used increased and assembly manhours increased too, resulting in the increase of the manufacturing cost. In the method of employing the ink for selective plating, on the other hand, there was a defect that the boundary between the base and the inked portion by transcribing was obscure and the process was complicated. When the surface of the base which patterns are formed thereon is curved or irregular, transcribing of the ink for selection plating was not well performed.